APIs simplify all that by limiting outside program access to a specific set of features—often enough, requests for data of one sort or another. Feel free to think of them as doors, windows or levers if you like. Whatever the metaphor, APIs clearly define exactly how a program will interact with the rest of the software world—saving time, resources and potentially nasty legal entanglements along the way.

APIs simplify all that by limiting outside program access to a specific set of features—often enough, requests for data of one sort or another. Feel free to think of them as doors, windows or levers if you like. Whatever the metaphor, APIs clearly define exactly how a program will interact with the rest of the software world—saving time, resources and potentially nasty legal entanglements along the way.